'The Avengers' actress - whose divorce from Ryan was finalized in 2011 after four years together - is said to be convinced he cheated on her with the 'Gossip Girl' star while they were still married and was distraught over the couple's recent nuptials.

A source told the National Enquirer: "Even though there is no evidence behind it, Scarlett has convinced herself that Ryan cheated on her with Blake.

"She's incredibly bitter about it. In a way, Scarlett feels like Blake actually stole Ryan from her, because it was when he started shooting 'Green Lantern' with Blake in 2010 that everything fell apart."

The 27-year-old actress was shocked to discover the couple had thrown a secret wedding reception in South Carolina on September 9 and was especially hurt Ryan remarried so quickly, after only a year of dating Blake.

The insider added: "Ryan and Blake's wedding has brought back a lot of pain for Scarlett. She's sure that Blake deliberately seduced Ryan, even though she knew he was attached at the time.

"On top of that, she feels like it's a huge slap in the face that Ryan would remarry this fast. Scarlett is happy and dating, but she assumed he would wait a few years before he tied the knot again."

Scarlett - who is currently romancing advertising executive Nate Taylor - has spoken candidly about her marriage to Ryan in the past.

She said: "It was a beautiful thing. The falling in love and getting married and making that commitment ... I think it's nice to know that you're capable of loving somebody in that way. I think it's a rare opportunity."